#include <unistd.h>
#include <string.h>
#include <errno.h>

int getlogin_r(char *name, size_t size)
{
    char *logname = getlogin();
    if (!logname) return ENXIO; /* or...? */
    if (strlen(logname) >= size) return ERANGE;
    strcpy(name, logname);
    return 0;
}
